Cold chamber pressure casting machine

ABSTRACT

A cold chamber pressure casting machine includes a mold charge injector, a melting or heat retaining crucible and a piston pump extending into the crucible and connected to the injector, the piston pump having a pump chamber communicating with a feed opening which is beneath the level of melt in the crucible. A displacement means is operatively associated with the melt in the crucible to control the level thereof, and a control means controls operation of the displacement means. A melt level feeler is positioned in the crucible in the range of the melt surrounding the piston pump, and influences operation of the control means. The displacement means may comprise a solid body which may be inserted into or retracted from the melt, or may comprise an inverted bell means connected to a source of fluid under pressure and communicating with the melt in the crucible. A float may be provided in the bell. The melt level feeler may comprise one or more electrodes, a pressure responsive means connected to a pressure fluid type operator of a control valve, or a float operated switch.

United States Patent [72] Inventor AlfredNef Uzwil, Switzerland 2|AppLNo. 773,464

[22] Filed Nov.5,1968

[45] Patented [73] Assignee July 6, 1971 Gebruder Buhler A. G.

, Uzwill, St. Gall, Switzerland {32] Priority Nov. 8, 1967 [33]Switzerland [54] COLD CHAMBER PRESSURE CASTING MACHINE 3,412,899 11/1968Sutter 164/115UX Assistant Examiner-R. Spencer Annear Attorney-McGlcwand Toren ABSTRACT: A cold chamber pressure casting machine includes amold charge injector, a melting or heat retaining crucible and a pistonpump extending into the crucible and connected to the injector, thepiston pump having a pump chamber communicating with a feed openingwhich is beneath the level of melt in the crucible. A displacement meansis operatively associated with the melt in the crucible to control thelevel thereof, and a control means controls operation of thedisplacement means. A melt level feeler is positioned in the crucible inthe range of the melt surrounding the piston pump, and influencesoperation of the control means. The displacement means may comprise asolid body which may be inserted into or retracted from the melt, or maycomprise an inverted bell means connected to a source of fluid underpressure and communicating with the melt in the crucible. A float may beprovided in the bell. The melt level feeler may comprise one or moreelectrodes, a pressure responsive means connected to a pressure fluidtype operator of a control valve, or a float operated switch. a

PATENTEU JUL SIS?! 3,591. 052

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WWW 7M1 HTTORNEH COLD CHAMBER PRESSURE CASTING MACHINE BACKGROUND OF THEINVENTION Italian Pat. No. 557,374 discloses a piston pump with anantechamber which is arranged in a furnace or the like for maintainingthe heat in the material to be cast. Feed openings serve to supply themelt from the antechamber into the pump chamber. A melting crucible isarranged in another furnace, and a melt conveyor pipe interconnects thelower portion of the melting crucible and the antechamber. In themelting crucible, there is arranged an immersion body which serves tomove the melt from the melting crucible into the antechamber, thisimmersion body being operated by means of a spindle.

By means of this melt conveyor pipe, the piston, with its antechamber,associated with the cold chamber pressure casting machine, and themelting crucible, form communicating vessels as long as sufficient meltis displaced by the immersion body. This arrangement has disadvantages.With each feed of the pump after each delivery, considerablefluctuations in level occur in the antechamber. These level fluctuationsin the antechamber can be equalized only very slowly, due to the longmelt conveyor pipe. There is no direct influence on the melt level inthe antechamber by the means for displacing the melt. Depending on thetime interval from one pump feed to the next, the melt level in theantechamber differs from that in the melting crucible. Thus, theprerequisite that the melt level in the antechamber be maintainedconstant during operation of the piston pump is not assured.

Additionally, a separate furnace is required for the piston pump whichis arranged outside the melting crucible. The melt conveyor pipe alsomust be heated. Thus, the maintenance of a constant temperature in allparts carrying the melt is difficult. The melt conveyor pipe has acoupling which is arranged beneath the operating level of the melt. Inorder to disassemble the pump from the heat maintaining furnace, thiscoupling must be disengaged, and this requires evacuation of the meltingcrucible. During disassembly of the pump, there is the danger that apart of the melt still contained in the antechamber will be discharged.

SUMMARY OF THE INVENTION This invention relates to cold chamber pressurecasting machines and, more particularly, to a novel and improved coldchamber pressure casting machine having novel means controlling the meltlevel adjacent the inlet opening to the pump chamber forming part of apiston pump for feeding a mold charge injector.

The objective of the present invention is to eliminate theabove-mentioned disadvantages of known cold chamber pressure castingmachines. For this purpose, the cold chamber pressure casting machine ofthe invention comprises the combination of a melt level feeler in therange of the melt surrounding the piston pump, displacement means actingon the melt surrounding the piston, and a control, for the operation ofthe displacement means, which is influenced by the level feeler.

The cold chamber pressure casting machine of the present invention hasmany advantages. The level feeler is influenced by the melt level, whichdetermines the dosing accuracy of the piston pump. The displacementdevice or means is effective on the melt surrounding the piston pump.Thus, a slow equalization of the melt level is avoided. Since themelting crucible has a large volume, compared to the pump chamber, themelt level varies only slightly with each pump feed. Thus, greataccuracy ofthe dosing of the piston pump is achieved.

The displacement device can be designed as an immersion body dippinginto the melting crucible, and this body is closed on all sides, atleast in the range of its contact with the melt. For the operation ofthe immersion body, there can be provided a piston moving in a cylinder,and a spring associated with the piston which biases the piston to thereturn position. If there is no pressure on the piston, lowering of theimmersion body into the melt is prevented by the spring.

The displacement device or means can also be in the form of an insertwhich is fixedly mounted in the melting or heatretaining crucible, andhaving a closure above the operating level of the melt thus to form achamber that can be supplied with pressure gas. An open end of thisinsert is disposed below the maximum displacement level of the melt.Since this insert has a small exposed surface, heat losses are avoidedto a great extent. The open end of the insert can be provided with arestriction in order to avoid building up transient processes during thelevel regulation, while still providing the possibility of regulation ofa plurality of dosing deliveries from the crucible.

Furthermore, the insert may be provided with a piston designed as afloat which closes the open end when the maximum displacement level isreached, and thus prevents issuance of pressure gas into the meltingcrucible.

A control influenced by the melt level feeler means, and effecting theadmission of pressure gas to the insert, can be provided with a pressurelimiting device, adjoining the chamber of the insert, and supplied withpressure gas to insure automatic limitation of the maximum meltdisplacement. This arrangement also prevents escape of pressure gasthrough the open end of the insert.

The insert can also have a measuring chamber which is connected, on theone hand, with the insert in the range of the open end of the latterand, on the other hand, with the pres sure limiting means. The maximummelt displacement in the insert thus can be determined independently ofthe specific gravity of the melt.

In order to supply pressure gas to the insert, there can be arranged, inthe insert, a pressure gas feed pipe connected to a pressure gas line,and the opening of this feed pipe is in the range of the maximumdisplacement of the melt. A pressure followup valve, servingconcurrently as a level feeler and as a control influenced by it, andfixed in accordance with the operating level and the specific gravity ofthe melt, is connected with the pressure gas line.

An object of the invention is to provide an improved cold chamberpressure casting machine.

A further object of the invention is to provide such a cold chamberpressure casting machine which is free of the disadvantages of prior artcold chamber pressure casting machines while being greatly simplified inconstruction and improved in efficiency.

A further object of the invention is to provide such a cold chamberpressure casting machine which includes a mold charge injector, amelting or heat-retaining crucible, and a piston pump extending into thecrucible and connected to the injector, the piston pump having a pumpchamber communicating with a feed opening which is beneath the level ofmelt in the crucible.

Another object of the invention is to provide such a cold chamberpressure casting machine including the displacement means operativelyassociated with the melt in the crucible to control the level thereof.

A further object of the invention is to provide such a cold chamberpressure casting machine including control means controlling operationof the displacement means,

A further object of the invention is to provide such a cold chamberpressure casting machine including melt level feeler means positioned inthe crucible in the range of the melt surrounding the piston pump andinfluencing operation of the control means.

A further object of the invention is to provide such a cold chamberpressure casting machine in which equalization of the melt level in thepump chamber and in the crucible is effected very rapidly, and in whichthe level varies only slightly with each feed of the pump.

Another object of the invention is to provide such a cold chamberpressure casting machine assuring great dosing accuracy of the pistonpump.

For an understanding of the principles of the invention, reference ismade to the following description of typical embodiments thereof asillustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. I is a vertical sectional view of a first embodiment of coldchamber pressure casting machine, with a feeding device and control, inaccordance with the invention;

FIG. 2 is a view, similar to FIG. ll, illustrating a second embodimentof a cold chamber pressure casting machine in accordance with theinvention;

FIG. 3 is a partial sectional view of a third embodiment of cold chamberpressure casting machine, in accordance with the invention, illustratinga part of a'crucible similar to that shown in FIG. 2;

FIG. 4 is a view, similar to FIG. 3, of a fourth embodiment of coldchamber pressure casting machine in accordance with the invention; and

FIG. 5 is a view, similar to FIGS. 3 and 43, of a fifth embodiment of acold chamber pressure casting machine in accordance with the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. ll, acasing I has arranged therein a crucible 2 containing melt 3, andsuitable heating means may be provided in operative association withcrucible 2 to retain the heat in melt 3. A piston pump 4 extends intocrucible 2 through an opening 5 of a partial covering 6 of the crucible.Piston pump A has a piston receiving bore serving as a pump chamber 7,and has at least one feed opening 8 arranged beneath the operating levelof melt 3. A duct 9 connects pump chamber 7 with an outlet trough 10serving to supply melt to a mold charge injector cylinder ll of apressure casting machine which has not been shown in detail. A pumppiston 12, movable in pump chamber 7, is connected by a bar or pistonrod 13 with an operating piston 14 that may have pressure applied to itsopposite sides. Operating piston M is displaceable in a cylinder 16secured on an upright support 15.

An immersion body il7, which has a closed formation in the range of itscontact with melt 3, is connected, through the medium of a bar or rod113, with a regulating piston 19 that can be subjected to gas underpressure on one side. Regulating piston 19 is mounted for displacementin a cylinder 30, which is mounted on an upright support 31. Acompression spring 32, biasing regulating piston 18 to the return orupper position, is arranged between piston 18 and the lower end of thecylinder 34D, spring 32 being prestressed.

A level feeler 33 extends into crucible 2 through a dielectric part 34of covering 6. The end of feeler 33 in crucible 2 is set to theoperating level of melt 3.

A suction line 38 extends from a tank 35, containing pres sure medium36, to the inlet of a pump 37. A reversing valve 39, having a reversingmagnet 40 and a biasing spring 411, is connected with pump 37 by asupply line 42 and with tank 35 by a return line 433. A supply line 44and a return line 4l5 connect reversing valve 45 to cylinder R6.

in addition, a regulating valve 46 is connected to pressure line 42, andhas an operating solenoid 47 and a biasing spring 48. A line 49 connectsregulating valve 46 with cylinder 30, and a relief valve 62 is connectedwith line 419 and thus with cylinder 30, and can be actuated by asolenoid 60 and a biasing spring 61. A one-way pressure relief valve 64is connected in an intermediate line 63 connecting relief valve 62 toreturn line &3. Reversing solenoid 40 is connected through conductors 65and 66 with the machine control 67 of the pressure casting machine,which latter is connected to a source 68 of electrical potential.

The elements provided for control of the level regulating will now bedescribed. A supply device 72 is connected to a current source 63through conductors 70 and 71. Supply device 72 has connected therewithan amplifier 73, a relay switch 74% and a main switch 75. Solenoid MD ofrelief valve 62 is connected with supply device 72 through a pair ofmake or front contacts 76 of main switch 75 and through a control line77. A return line 78 closes its circuit to supply device 72. Amplifier73 is grounded. A measuring line 79 connects level feeler 33 toamplifier 73, and amplifier 73 is connected, on the one hand, with onecontact of an additional pair of make or front contacts'titl of the mainswitch 75 and, on the other hand, with a terminal of a relay coil 82.The other terminal of relay coil 82 is connected with the second contactof this additional pair of make or front contacts 30.

Relay coil 82 controls a changeover switch 33 connected, on the supplyside, with supply device 72 and including a normally open or frontcontact connected by a line ml to one termine] of solenoid 437 ofregulating valve 46. The other terminal of solenoid 47 is connected tothe return line 73 leading to supply device 72.

The embodiment of the invention shown in FIG. 1 operates in a mannerwhich will now be described. Pump 37 delivers pressure medium 36 fromtank 35 into pressure line 42 and, through reversing valve 39 and fluidpressure line -55, to the chamber of cylinder lib beneath piston 114.The chamber of cylinder 16 above piston M is connected through line Ml,reversing valve 39 and return line $3 with tank 35 and is thus free ofpressure. Piston M lifts pump piston 12 into the upper dead centerposition. Melt flows through feed opening or openings 8 into pumpchamber 7 and duct 9 until the melt level in duct 9 is equalized withthe melt level in crucible 2 surrounding piston pump 3.

After the divided mold of the pressure casting machine, which has notbeen shown, is closed, solenoid 4th is energized by machine control 67and actuates reversing valve 39 against the bias of spring 4111. Pump 37now delivers pressure medium 36 through pressure line 42, valve 39 andline M to cylinder 16 above piston 14. Piston 14 thus moves pump pistonl2 down through the piston rod 113. Pump piston 12 closes feed openingor openings 8, and thus pump chamber 7, from crucible 2, so that no melt3 can now flow from pump chamber 7 into crucible 2. The melt is forcedthrough duct 9 and outlet trough Ml into charging device ll ll.

After the melt has been supplied to the pressure casting machine,machine control 67 deenergizes solenoid 4N) and spring til movesreversing valve 39 back into the rest position shown in FIG. )1.Pressure medium 36 delivered by pump 37 through pressure line 72 toreversing valve 39 now flows through line 45 and into the chamber ofcylinder to beneath piston M, and pump piston 12 is moved into the otheror upper dead center position. The melt supplied to charging device 111is forced, by the charging unit of the pressure casting machine, intothe mold cavity.

A constant dosing accuracy of piston pump 45 with a fixed stroke of pumppiston 12 is ensured only with a constant operating level of the melt 3surrounding the pump il. This constancy of the level is attained in amanner which will now be described.

Melt flowing from crucible 2 into piston pump 5, after supplying of thepressure casting machine has been completed, effects a drop of the meltsurface or level in crucible 2, and this must be compensated. Uponstarting the pressure casting machine, main switch 75 is closed andsolenoid as is energized, from current supply device 72, through frontcontacts 76 of switch 75 and supply line 77, so that relief valve 62closes. When switch 75 is closed, relay coil 82 is connected to theoutput of amplifier 73 through front contacts 8th. A drop in the levelof melt 3 influences amplifier 73 through level feeler 33. Amplifier 73excites relay 82 to close switch 33. Solenoid 47 is energized responsiveto closing of switch 33, and regulating valve is opened against the biasof spring 48.

Regulating valve 46 and regulating line 419 of regulating piston 19 arenow supplied with pressure medium as by pump 37, the pressure mediumacting against the bias of spring 32. Immersion body 117 thus is loweredinto crucible 2 through the piston rod Ml connected to piston 19. Animmersion body 117 dips into melt 3, the melt is displaced, resulting ina rise in the level of melt 3. When the level attains the desiredoperating level, level feeler 33, which is set to this desired operatinglevel, influences amplifier 73 to deenergize relay coil 82 and switch 83opens. Solenoid 47 is deenergized and spring 48 biases regulating valve46 into the closed or rest position shown in FIG. 1. The supply ofpressure medium 36 from pressure line 42 through regulating line 49 intocylinder 30 is interrupted. Immersion body 17 is thus retained in theposition set for maintaining the operating level of melt 3, suchretention being effected,.on the one hand, by spring 32 and, on theother hand, by pressure medium 36 in cylinder 30.

After a working cycle of the pressure casting machine has been completedand the mold is reclosed, machine control 67 effects another feed ofmelt 3 to charging device 11 through the medium of piston pump 4, asexplained above. By opening main switch 75, solenoids 47 and 60 aredeenergized, and regulating valve 46 and relief valve 62 are biased bytheir respective springs 48 and 61 into the rest position. The supply ofpressure medium 36 to regulating line 49 into cylinder 30 isinterrupted. Pressure medium 36 flows through regulating line 49, reliefvalve 62, one-way valve 64 and return line 43 into tank 35. Compressionspring 32 biases regulating piston 19, and thus the immersion body 17,back into the rest position. The level of the melt 3 in crucible 2drops, and melt can be supplied into crucible 2.

Since level feeler 33 is influenced by the melt 3 directly surroundingpiston pump 4, and as the immersion body 17 lifts this melt directly,equalization is effected rapidly and without overriding, which couldhappen with a prolonged flow. Since crucible 2 has a large volume,compared to the volume of pump chamber 7 which is fed directly fromcrucible 2, the melt level varies only slightly during feeding operationof the pump. A great dosing accuracy of piston pump 4 is thus ensured,even in an equalization with a somewhat greater time constant.

If current source 69 fails, regulating piston 19 is relieved of pressurethrough relief valve 62 because of the immediate deenergization ofsolenoid 62, and compression spring 32 biases regulating piston 19, andthus immersion body 17, into the rest position. The level of melt 3drops, in any case. Accidents, due to rising of the melt above theoperating level, are thus positively prevented. For the same purpose,main switch 75 also serves as an emergency switch.

In the second embodiment of the invention, shown in FIG. 2, the partsfor actuating piston pump 4, as well as the pump itself, correspond tothose shown in FIG. 1 and. described above. An insert 91 which isfixedly mounted in crucible 2 and secured on at least partial covering 6thereof, serves as a dis placement device or means. Above the operatinglevel of melt 3, insert 91 has a closure 92 and, below the maximumdisplacement level of melt 3, insert 91 has an open end 93. A chamber94, which can be supplied with a pressure medium such as a gas underpressure or an inert fluid under pressure, is formed within insert 91and beneath closure 92. Two electrodes 95, 96 extend partly into melt 3,and consist of electric resistance material. These electrodes extendthrough a dielec tric part 34 in which they are fixedly mounted. Thebottom end of a third electrode 97, also mounted in dielectric part 34,is slightly above the operating level of melt 3.

Chamber 94 is connected to a blower 100 through a pressure gas pipe 98and a throttle 99. A gas pressure regulating valve 101 is connected topressure gas pipe 98 and is provided with an exhaust 102. Valve 101 canbe controlled by a solenoid 103. In addition, a pressure switch 104 isconnected to pressure gas pipe 98 and has associated therewith a hand ormanual control 105.

A pair of front or make contacts 113 of pressure switch 104, anintermediate line 114, a back or rest contact 115 of a safety switch116, a distribution line 117 and an electric bridge connection areconnected to a current source 111 through a supply line 112. A returnline 118 leads from the bridge connection to current source 111. Thebridge connection includes a first leg or branch, consisting of aresistance 121 and a diode 122, connecting diagonal point A todistribution line 117. The bridge connection further includes a secondleg or branch, consisting of a resistance 123 and a diode 124,connecting diagonal point B to distribution line 117. A third leg orbranch extends from diagonal point A to return line 118, this third legor branch including the electrodes and 96. The fourth leg or branch ofthe bridge connection extends from diagonal point B to the groundedreturn line 118, and includes a balancing resistance 125.

The bridge diagonal extends from point or junction A to point orjunction B and includes the collector or armature circuit of a motor 128having a field coil 129. One end of field coil 129 is connected througha diode 130 to distribution line 117. The other terminal of fieldwinding 129 is connected directly to the grounded return line 118. Acontrol circuit is connected in parallel with the bridge circuit, andincludes solenoid 103, an adjustable limiting resistance 131 and arheostat or potentiometer 132, this control circuit being connectedbetween distribution line 117 and grounded return line 118. Theadjustable sliding contact 133 of rheostat 132 is mechanically connectedwith the shaft of motor 128.

A relay coil 134 of safety switch 116 has one end connected tointermediate line 1 14 and its other end connected, by a line 135, withelectrode 97. This safety circuit can be closed, at a high melt level,by electrode 97, melt 3, electrode 95, and grounded return line 118connected to current source 11. Another safety circuit has one endconnected to current source 111 and includes back or rest contacts 136of pressure switch 104, a branch line 137, a signal horn 138 andgrounded return line 118. Line 137 is also connected to the front ormake contact of safety switch 116.

The embodiment of the invention shown in FIG. 2 operates in the mannerwhich will now be described. To set the operating level, balancingresistance 125,in the bridge leg or arm extending from junction point Bto grounded return line 118, is adjusted until the effective resistancevalue is equal to the sum of the resistances of electrode 95, melt 3 andelectrode 96. When this occurs, the voltage gradient from junction pointA to junction point B is zero, so that the collector circuit of motor128 has no current flowing therethrough. To set the maximum level ofmelt displacement, the excitation of solenoid 103 is adjusted byadjusting limiting resistance 131, with rheostat 132 shorted out, andtaking into account the characteristic of gas pressure regulating valve101 and the specific gravity of melt 3. Crucible 2 is filled with melt 3to a level corresponding approximately to the operating level.

By operating pressure switch 104, the bridge connection is connected tocurrent source 111 through contacts 113. If the sum of the resistancesfrom junction point A to return line 118 is greater, at the fillinglevel than at the operating level, and thus with respect to balancingresistance 125, there is a voltage gradient in the path 117-A which isgreater than the voltage gradient in the path 117-B, and thus there is avoltage gradient, across the bridge diagonal, from junction point A tojunction point B. Motor 128 thus is excited and gas pressure regulatingvalve 101 is adjusted to a higher pressure value. Accordingly, pressuregas at higher pressure is supplied to chamber 94, so that melt 93 isdisplaced from chamber 94 to raise the level of the melt 3 in thecrucible 2. Thereupon, the sum of the resistances from electrode 95through melt 3 to electrode 96 is correspondingly decreased. When thelevel of the melt has reached the operating level, the sum of theseresistances equals the value of the balancing resistance 125. Thevoltage gradient across bridge diagonal A-B is thus reduced to zero andno current flows through the armature 128 of the motor. The start of thepressure casting machine effects, through machine control 67, supplyingof melt 3 by piston pump 4 to charging device 11, as described inconnection with the embodiment of the invention shown in FIG. 1. Thelevel of melt 3 in crucible 2 drops. The next rise of the melt level tothe operating level is effected in the same manner as the rise in themelt level from the filling level to the operating level, by increasingthe pressure of the gas supplied to chamber 94.

When the maximum displacement level of melt 3 has been attained,pressure switch 104 is brought, by the maximum gas pressure, into therest position to open front or make contacts 113 and close back or restcontacts 136. Solenoid 1113 of gas pressure regulating valve 161 is thusdeenergized, so that this valve moves back to the pressure setting zerowith the pressure gas discharged from chamber 94 through exhaust port102. At the same time, the closed contacts 136 energize signal horn 138to indicate that melt must be supplied to crucible 2. Pressure switch1114 can be brought into the rest position by the manual control 1115.

When melt is supplied to crucible 2 during operation of the castingmachine, the level of melt 3 in the crucible rises beyond the operatinglevel. The resulting lower resistance from junction point A to returnline 1118, with respect to the fixed resistance from junction point B toreturn line 1111, effects an unbalance of the potential at the oppositeends of the diagonal A-B, and a voltage gradient is thus formed fromjunction point B to junction point A. Motor 125 is thus energized in adirection which is reversed with respect to that described above. Motor126 controls sliding contact 133, so that the resistance betweenlimiting resistance 131 and sliding contact 133 of rheostat 132 isincreased. The current, and thus the excitation, of solenoid 103 isdecreased, and gas pressure regulating valve 1111 is thus set to a lowerpressure value. Pressure is relieved from chamber 341 through'exhaustport 102 of valve 101 until the pressure in chamber 96 equals thesetting of valve 161. At the same time, the displacement level of meltin chamber 94 increases, thus effecting a drop of the melt level incrucible 2. The sum of the resistances from junction point A to returnline 1118 increases. When the melt level has dropped to the operatinglevel, the sum of these resistances corresponds to the setting ofbalancing resistance 125. The voltage gradient from junction point B tojunction point A is reduced to zero, so that no current flows throughrotor or armature 128 of the motor.

When the melt level rises to a level outside the regulating range of thecontrol, relay coil 1341 is energized over a circuit extending fromreturn line 116 through electrode 95, electrode 96, line 135, relay'coil 134, line 114, front contacts 113 and line 112 to source 111.Safety switch 116 is thus operated to disengage contact 115 and toengage contact 1311v This deenergizes solenoid 1113 of pressureregulating valve 161 and energizes signal horn 1311.

Due to the small free surface of insert 91, heat losses are avoided to agreat extent. If blower 11111 fails, or if the pressure gas pipe 911leaks, the displacement level of melt 3 in chamber 94 rises, resultingin a drop of the melt level in crucible 2. The excitation of solenoid163 of gas pressure regulating valve 161 can be set easily to themaximum displacement level of melt 3 in chamber 941 using limitingresistance 131. Pressure switch 166 likewise limits this maximum meltdisplacement, so that the discharge of pressure gas through the open end193 of insert 91 is positively prevented.

1n the third embodiment of the invention, shown in FIG. 3, the open endof insert 91 has a restricted orifice 1 16. A piston 1417, designed as afloat, is provided in insert 91, and has a protuberance or extension 148facing orifice 146. Due to the throttling effect, building-up processesare avoided during level regulation by the constriction 1416, withoutnarrowing the regulating range. Piston 14-7, through its extension 1 18,prevents escape of gas under pressure from insert 91 through orifice1416 when the level of the displaced melt 3 drops below the maximumdisplacement level set on gas pressure regulating valve 101. Piston 1417thus serves as a safety device against the escape of gas under pressurethrough restriction 166 and independently of the control.

1n the fourth embodiment of the invention, as shown in F 16. 41, insert91 has, in addition to chamber 941, a measuring chamber 151 whichcommunicates with chamber 94 adjacent the open end 93 and particularlyin the range of the maximum melt displacement. Above the operatinglevel, measuring chamber 151 has a closure 152. As a melt level feelermeans, a pipe 156 is connected with the cover 6, and this pipe has aclosed upper end and an open lower end 153 in the range of melt 3. Pipe154 extends into melt 3 and is supplied with pressure gas through a portin its closed upper end. As a source of pressure gas, particularlyprotective gas at a constant pressure, there is provided a pressure gastank 156 associated with the pressure reducing valve 155. A gas pipe 157is connected to pressure reducing valve and to feeler pipe 154 through adiaphragm 159 and a measuring pipe 1611. Pressure gas pipe 157 is alsoconnected to a regulating valve 162 which can be controlled, on the onehand, mechanically, for example by a spring 163, and, on the other hand,by a pneumatic operating element 166 connected to measuring pipe 166.

An intermediate pipe 165 connects regulating valve 162 to a reversingvalve 166. Regulating valve 162 has flow ducts arranged therein in sucha manner that, in one switching position, a connection is establishedfrom pressure gas pipe 157 to intermediate pipe 165 and, in the otherswitching position, a connection is established from intermediate pipe165 to an exhaust port 167. For the control of reversing valve 166, thelatter has associated therewith a first control element 176, in thiscase a mechanical control element, and a second control element 171which is a pneumatic control element. A displacer pressure pipe 172extends from reversing valve 166 into chamber 94 of insert 91, and arelief pipe 173 extends into measuring chamber 151. A control pipe 1741is branched from relief pipe 173 to pneumatic control element 171 ofreversing valve 166. Reversing valve 166 has, in one switching position,a closure for intermediate pipe 165 and flow ducts from displacerpressure pipe 172 and relief pipe 173 to exhaust port 177. in the otherposition, reversing valve 166 has closures for relief pipe 173 andexhaust port 177, on the one hand, and a flow duct from intermediatepipe 165' into displacer pressure pipe 172, on the other hand.

The method of operation of the embodiment of the invention shown in FIG.1 will now be described. By actuating reversing valve 166, chamber 9 1of insert 91 is connected with regulating valve 162. Pressure gas flowsfrom pipe 157 through diaphragm 151) and measuring pipe 161] into pipe15 1, serving as a level feeler, so that melt is displaced from pipe156. The gas pressure in measuring pipe 166 should correspond to thestatic pressure of the melt column between opening 153 and the operatinglevel of the melt 3 in crucible 2. Variations of the operating levelinfluence the pneumatic operating element 164 of regulating valve 162.1f the melt level drops below the operating level, the gas pressure inmeasuring pipe drops, due to the increasing escape through melt 3, andregulating valve 162 opens, under the bias of spring 163, the connectionfrom pressure gas pipe 157 into intermediate pipe 165. Pressure gas issupplied to chamber 94 and melt is displaced from the latter, so thatthe melt level in insert body 91 drops and the melt level in crucible 2rises. The gas pressure in measuring pipe 1611 rises with the increasinglevel of melt 3 in crucible 2. When the melt level has reached theoperating level, regulating valve 162 closes both connections providedtherein.

When the maximum displacement level is attained in chamber 941, pressuregas flows from the latter into measuring chamber 151, and this pressuregas acts, through control pipe 174, on control element 171 which movesreversing valve 166 back into the rest position. Pressure gas isdischarged from chamber 941 and measuring chamber 151 through reliefpipe 173 and exhaust port 177. The levels of the melt 3 in crucible 2and in chamber 941 are thus equalized. lf necessary, reversing valve 166can also be moved into the rest position by hand control, as indicatedat 1711.

if melt is supplied to crucible 2 before the maximum displacement levelis reached, with reversing valve 166 being opened, the melt level risesin crucible 2 beyond the operating level. The pressure in measuring pipe1611 is correspondingly increased, and valve 162 opens, under theinfluence of operating element 164, the connection from intermediatepipe to exhaust port 167. The gas in chamber 941 is discharged throughexhaust port 167, and the melt level in insert Q1 rises so that the meltlevel in crucible 2 drops. The gas pressure in measuring pipe 160 isdecreased again. When the melt level in crucible 2 has dropped to theoperating level, regulating valve 162 closes both connections providedtherein. The maximum displacement of melt 3 from insert 91 into crucible2 is determined by the position of the open end 93 of measuring chamber151, and is thus independent of the specific gravity of melt 3 and ofthe pressure setting of regulating valve 162.

In the fifth embodiment of the invention, shown in FIG. 5, a speciallyconstructed insert 91 is used in the cold chamber pressure castingmachine shown in FIG. 4. This embodiment of the invention also includescrucible 2, piston pump 4 inserted therein and outlet trough leading tothe charge injection device 11. ln this special insert 91, there isprovided a pressure medium supply line 181 whose lower end 182 opensinto chamber 94 of insert 91 in the range of the maximum displacement ofmelt 3 from chamber 94 into crucible 2. A float 183 is positioned incrucible 2 and has a rest position which is slightly above the operatinglevel of melt 3. The switching element of a float switch 204 isconnected with float 183.

A pressure followup valve 184, with an adjustment element 185 and apneumatic control element 186, is connected to pressure gas pipe 157.Through an intermediate line 187, valve 184 is connected with areversing valve 191 which is controlled by a solenoid 188 and a spring189, and is provided with an exhaust port 190. A control line 192 isbranched from intermediate line 187 and connected to pneumatic element186 of valve 184. A line 193 connects reversing valve 191 to pressuremedium supply line 181 in insert 91. Chamber 94 of insert 91 isconnected, through a pipe 194 in its upper closure 92, with reversingvalve 191. In addition, a pneumatic operat ing element 195 of a switch196 is connected to pipe 194.

A solenoid 188 is associated with reversing valve 191 and is connectedto current source 197 through a circuit including [supply conductor 198,front or make contacts 199 of switch 200, an intermediate conductor 201,solenoid 188, back or rest contacts 202 of float switch 204 associatedwith float 183, and a return conductor 205. Another circuit is provided,and comprises a current source 206, a supply conductor 207, a pair ofmake or front contacts 208 of pressure switch 196, a return coiiductor209 and a signal horn 210.

For all the different embodiments of the invention, the problem to besolved consists in keeping the melt level constant in a melting ormelt-heat-retaining crucible associated with a pressure casting machine,in order to ensure constant amounts of melt for feeding this machine bya piston feed pump of fixed stroke and which is inserted into tliecrucible, While, in the embodimeg ts previously described, the solutionof the problem consists displacing melt by suitable means dipping intothe melt in varying depth, or acting on the melt in different ways,these different means being controlled by a level feeler whose constantreadjustment requires a control influencing the means, the followingconditions were recognized for the embodiment of the invention shown inFIG. 5: on the one hand, the operating level should be constant withrespect to any point in the crucible 2. Consequently, the staticpressure at this point should be constant. On the other hand, so muchmelt always should be displaced by a pressure medium supplied through aclosed chamber 94 above an opening in the range of crucible 2, that theoperating level in crucible 2 is maintained constant. This means thatthe sum of the pressures above the melt and of the pressure mediumacting on it should likewise be constant. However, since the melt variesits level in chamber 94, the pressure of the pressure medium in chamber94 must also be varied.

The embodiment of the invention illustrated in FIG. 5 utilizes, for thispurpose, the following relations to meet the foregoing conditionsautomatically:

The static pressure of the opening 182 of pressure medium supply line181 into chamber 94 of insert 91, as resulting from the melt 3 incrucible 2, is p =Hk where k is the value of the specific gravity of themelt. For the operating level, there applies p =H,,Xk=Consmnt.

At the same time, the pressure of the melt 3 to be displaced, above theopening 182, acts on this opening from chamber 94 in insert 91, as alsodoes the gas pressure p,; on this melt. From this, there arises therelation p =p =haPk.

However, since H is always to be made equal to H by displacement of meltfrom insert 91, and therefore by the value It, and due to the increaseof p h and p; are variables. However, for the operation there appliesPMn Hn k PR+h k' Constant.

This means that, on the one hand, a constant gas pressure must bepresent at the opening 182 for supply of the pressure medium, that is,the pressure gas, through the pressure medium supply line 181 into theinsert 91 but that, on the other hand, and at the same time, thevariables h and p are set automatically to the constant summation valuep prl-hXk. The pressure followup valve 184 therefore can be adjustedsubstantially to the fixed pressure value H Xk. As long as the geometryof apparatus remains constant, this setting depends strictly on thespecific gravity of the melt.

Taking into account these physical conditions, the following operationis possible: reversing valve 191 is reversed upon energization ofsolenoid 188 through operation of switch 200. The connection frompressure followup valve 184 to opening 182 of pressure medium supplyline 181 is established. It can be assumed that the operating level H--Hof the melt 3 in crucible 2 has been reached. At the opening 182 tochamber 94 in insert 91 there act, simultaneously and in equilibrium,the fixed gas pressure H,,Xk from pressure followup valve 184 and, fromchamber 94, the sum of the pressures p ,+h k and, from crucible 2, thepressure H Xk.

After supplying of the pressure casting machine and refilling of pistonpump 4, the pressure H in crucible 2 drops to l-1,, so that H,Xk istherefore less than H Xk. Immediately, p +h k is greater than H 1 sothat an equalization of melt 3 from insert 91 into crucible 2 occurs insuch a manner that h, decreases to 11,, and H, increases to H With thedrop of h to h,, the pressure p drops to p There occurs instantly H,X k{h k.+ P less than H,,Xk=setting of the pressure followup valve 184.

Under the spring bias, pressure followup valve 184 therefore opens, withrespect to the lower gas pressure H, k in the pneumatic element 186.Pressure gas flows into pressure gas supply pipe 181 and bubbles intochamber 94, raising the pressure p, to thus displace melt 3 from chamber94 into crucible 2 until the level of melt 3, in crucible 2, has risenfrom 1'1 to H and the following new relation applies: H k=h lt=settingof the pressure followup valve 184. h is less than h gi l p is greaterthan p The pressure followup valve l84glosesj When the maximum meltdisplacemenf has been reached with respect to insert 91, the level ofthe displaced melt will be at the opening 182 of pressure medium supplyline 181, and

the gas pressure p prevailing in chamber 94, is i =H,,aPk.

Pressure switch 196, set to this pressure, is actuated to close thecontacts 208 and energize signal horn 210. Switch 200 is to be reversed.

lf melt is refilled as long as the normal operation continues, the meltlevel in crucible 2 rises beyond the operating level H,,. At H float 183will open the associated float switch 204, and solenoid 188, associatedwith reversing valve 191, is deenergized. Under the bias of spring 189,reversing switch 191 moves to the rest position. Pressure gas flowsimmediately from pressure medium supply line 181 and from chamber 94, sothat the level of the melt in chamber 94 rises while the level of themelt in crucible 2 drops. As soon as float switch 204 again closes,reversing valve 191 is brought into the operating position by thereenergized solenoid 188. Chamber 94, sealed from the exterior, andpressure medium supply line 181, to the pressure followup valve 184, areswitched, for the new level of regulation, to H =constant, due to thesetting of this valve H Xk -constant.

Such a cold chamber pressure casting machine has the advantage that theexpenditure for control is very low, since the measuring elements andcontrol elements are combined. In

llll

order to simplify the entire system, the setting device of the pressurefollowup valve can be calibrated both in values of the specific gravityof the melt and in concrete data of the melts to be processed (name ofthe alloy or its abbreviated symbol), as it is given to the machinist.That is, it can be provided with such a setting scale. For such acalibration, it is logical that the geometry of the crucible, the insertand the piston pump must be constant. Corresponding to the setting onthe pressure followup valve, the operating level is thus constant forany type of melt.

For the control of the reversing valve, it is possible to provide,instead of the electric circuit, a pneumatic control system branchingoff from the pressure gas pipe, with a pneumatic switch in place of theswitch 260 and a pneumatic float switch in place of the switch 204.Furthermore, instead of pneumatic displacement of the melt, hydraulicdisplacement also can be used with the same results, by using an inertfluid. it will be obvious that this can lead to certain changes whichare at the discretion of the designer.

it is essential, for the invention, that the piston pump associated withthe cold chamber pressure casting machine, the displacement means andthe melt level measuring means be arranged in one and the same cruciblein order to avoid the above-mentioned difficulties. Apart from thestable behavior of the overall device, this also results in a veryfavorable heat balance.

I claim:

l. in a cold chamber pressure casting machine with a mold chargeinjector, a melting or heat-retaining crucible, and an injectorsupplying piston pump extending into the crucible, the piston pumphaving a pump chamber communicating with a feed opening which is beneaththe level of the melt in the crucible: the improvement comprising, meltdisplacement means operatively associated with the melt in said crucibleto maintain the level thereof substantially constant in the range ofsaid piston pump; control means for controlling the effect of saiddisplacement means on the melt level; and melt level feeler meanspositioned in said crucible in the range of the melt surrounding saidpiston pump for providing an indication of the melt level to saidcontrol means.

2. in a cold chamber pressure casting machine with a mold chargeinjector, a melting or heat-retaining crucible, and an injectorsupplying piston pump extending into the crucible, the piston pumphaving a pump chamber communicating with a feed opening which is beneaththe level of the melt in the crucible: the improvement comprising, meltdisplacement means operatively associated with the melt in said crucibleto maintain the level thereof substantially constant in the range ofsaid piston pump; control means for controlling the effect of saiddisplacement means on the melt level; and melt level feeler meanspositioned in said crucible in the range of the melt surrounding saidpiston pump for providing an indication of the melt level to. saidcontrol means; said displacement means comprising an immersion bodymounted for lowering into said crucible and closed on all sides at leastin the range of its contact with the melt.

3. in a cold chamber pressure casting machine with a mold chargeinjector, a melting or heat-retaining crucible, and an injectorsupplying piston pump extending into the crucible, the piston pumphaving a pump chamber communicating with a feed opening which is beneaththe level of the melt in the crucible: the improvement comprising, incombination, melt displacement means operatively associated with themelt in said crucible to maintain the level thereof substantiallyconstant in the range of said piston pump; control means for controllingthe effect of said displacement means on the melt level; melt levelfeeler means positioned in said crucible in the range of the meltsurrounding said piston pump for providing an indication of the meltlevel to said control means; said displacement means comprising aninsert mounted in said crucible and including a lateral wall and aclosed upper end forming a pressure medium chamber having an open endbelow the maximum displacement level of the melt in a downwarddirection; and a pressure medium supply line connected to said insertand communicating with said pressure medium chamber; said control meansalso being for controlling flow of pressure medium through said supplyline to maintain the melt level constant in the range of said pistonpump.

4. in a cold chamber pressure casting machine with a mold chargeinjector, a melting or heat-retaining crucible, and an injectorsupplying piston pump extending into the crucible, the piston pumphaving a pump chamber communicating with a feed opening which is beneaththe level of the melt in the crucible: the improvement comprising, incombination, melt displacement means operatively associated with themelt in said crucible to maintain the level thereof substantiallyconstant in the range of said piston pump; control means for controllingthe effect of said displacement means on the melt level; melt levelfeeler means positioned in said crucible in the range of the meltsurrounding said-piston pump for providing an indication of the meltlevel to said control means; said displacement means comprising aninsert mounted in said crucible and including a lateral wall and aclosed upper end forming a pressure medium chamber having an open endbelow the maximum displacement level of the melt in a downwarddirection; a pressure medium supply line connected to said insert andcommunicating with said pressure medium chamber; said pressure mediumsupply line having, in the range of the maximum displacement level ofthe melt in a downward direction and in said insert, an opening; and apressure followup valve connected to said pressure medium supply lineand serving as said control means and said melt level feeler means; saidpressure followup valve maintaining the pressure in said pressure mediumchamber at a value corresponding to the hydraulic pressure of the meltbetween the nominal level of the melt in the crucible and said opening,said opening being at the lowest displacement level of the melt in saidcrucible.

5. in a cold chamber pressure casting machine, the improvement claimedin claim 2, including a piston mounted for movement in a cylinder andconnected to said immersion body; said control means supplying pressurefluid to one side of said piston to immerse said body in the melt.

6. In a cold chamber pressure casting machine, the improvement claimedin claim 5, including a spring biasing said piston in a direction toelevate said immersion body.

7. In a cold chamber pressure casting machine, the improve ment claimedin claim 3, including a piston designed as a float within said insert.

8. In a cold chamber pressure casting machine, the improvement claimedin claim 3, in which the open end of said insert is closed except for arestricted port.

9. in a cold chamber pressure casting machine, the improvement claimedin claim 3, including a piston, designed as a float, in said chamber.

10. in a cold chamber pressure casting machine, the improvement claimedin claim 3, in which said control means comprises a pressure limitingdevice connected to said pressure medium chamber.

111. In a cold chamber pressure casting machine, the improvement claimedin claim ill), in which said insert is formed with a measuring chamberhaving an open end communicating with said pressure medium chamberadjacent the open end of the latter, and having its opposite endconnected with and communicating with said pressure limiting device.

12. in a cold chamber pressure casting machine, the improvement claimedin claim 3, in which said pressure medium is a protective gas.

H3. in a cold chamber pressure casting machine, the improvement claimedin claim 4, in which said pressure medium supply line is a passageformed in the lateral wall of said insert; said opening communicatingwith said pressure medium chamber.

M. in a cold chamber pressure casting machine, the improvement claimedin claim 4, in which said pressure followup valve is set to a fixedpressure value.

15, In a cold chamber pressure casting machine. the im- 16 In a coldchamber pressure casting machine, the improvement claimed in claim 4. inwhich the upper wall of said provement claimed in claim 15, including afloat in said cruciinsert is formed with a closable opening above theoperating his in the range of the operating level of the melt andconlevel of the melt. trolling said closable opening.

1. In a cold chamber pressure casting machine with a mold chargeinjector, a melting or heat-retaining crucible, and an injectorsupplying piston pump extending into the crucible, the piston pumphaving a pump chamber communicating with a feed opening which is beneaththe level of the melt in the crucible: the improvement comprising, meltdisplacement means operatively associated with the melt in said crucibleto maintain the level thereof substantially constant in the range ofsaid piston pump; control means for controlling the effect of saiddisplacement means on the melt level; and melt level feeler meanspositioned in said crucible in the range of the melt surrounding saidpiston pump for providing an indication of the melt level to saidcontrol means.
 2. In a cold chamber pressure casting machine with a moldcharge injector, a melting or heat-retaining crucible, and an injectorsupplying piston pump extending into the crucible, the piston pumphaving a pump chamber communicating with a feed opening which is beneaththe level of the melt in the crucible: the improvement comprising, meltdisplacement means operatively associated with the melt in said crucibleto maintain the level thereof substantially constant in the range ofsaid piston pump; control means for controlling the effect of saiddisplacement means on the melt level; and meLt level feeler meanspositioned in said crucible in the range of the melt surrounding saidpiston pump for providing an indication of the melt level to saidcontrol means; said displacement means comprising an immersion bodymounted for lowering into said crucible and closed on all sides at leastin the range of its contact with the melt.
 3. In a cold chamber pressurecasting machine with a mold charge injector, a melting or heat-retainingcrucible, and an injector supplying piston pump extending into thecrucible, the piston pump having a pump chamber communicating with afeed opening which is beneath the level of the melt in the crucible: theimprovement comprising, in combination, melt displacement meansoperatively associated with the melt in said crucible to maintain thelevel thereof substantially constant in the range of said piston pump;control means for controlling the effect of said displacement means onthe melt level; melt level feeler means positioned in said crucible inthe range of the melt surrounding said piston pump for providing anindication of the melt level to said control means; said displacementmeans comprising an insert mounted in said crucible and including alateral wall and a closed upper end forming a pressure medium chamberhaving an open end below the maximum displacement level of the melt in adownward direction; and a pressure medium supply line connected to saidinsert and communicating with said pressure medium chamber; said controlmeans also being for controlling flow of pressure medium through saidsupply line to maintain the melt level constant in the range of saidpiston pump.
 4. In a cold chamber pressure casting machine with a moldcharge injector, a melting or heat-retaining crucible, and an injectorsupplying piston pump extending into the crucible, the piston pumphaving a pump chamber communicating with a feed opening which is beneaththe level of the melt in the crucible: the improvement comprising, incombination, melt displacement means operatively associated with themelt in said crucible to maintain the level thereof substantiallyconstant in the range of said piston pump; control means for controllingthe effect of said displacement means on the melt level; melt levelfeeler means positioned in said crucible in the range of the meltsurrounding said piston pump for providing an indication of the meltlevel to said control means; said displacement means comprising aninsert mounted in said crucible and including a lateral wall and aclosed upper end forming a pressure medium chamber having an open endbelow the maximum displacement level of the melt in a downwarddirection; a pressure medium supply line connected to said insert andcommunicating with said pressure medium chamber; said pressure mediumsupply line having, in the range of the maximum displacement level ofthe melt in a downward direction and in said insert, an opening; and apressure followup valve connected to said pressure medium supply lineand serving as said control means and said melt level feeler means; saidpressure followup valve maintaining the pressure in said pressure mediumchamber at a value corresponding to the hydraulic pressure of the meltbetween the nominal level of the melt in the crucible and said opening,said opening being at the lowest displacement level of the melt in saidcrucible.
 5. In a cold chamber pressure casting machine, the improvementclaimed in claim 2, including a piston mounted for movement in acylinder and connected to said immersion body; said control meanssupplying pressure fluid to one side of said piston to immerse said bodyin the melt.
 6. In a cold chamber pressure casting machine, theimprovement claimed in claim 5, including a spring biasing said pistonin a direction to elevate said immersion body.
 7. In a cold chamberpressure casting machine, the improvement claimed in claim 3, includinga piston designed as a float within said insert.
 8. In a cold chamberpressure casting machine, The improvement claimed in claim 3, in whichthe open end of said insert is closed except for a restricted port. 9.In a cold chamber pressure casting machine, the improvement claimed inclaim 8, including a piston, designed as a float, in said chamber. 10.In a cold chamber pressure casting machine, the improvement claimed inclaim 3, in which said control means comprises a pressure limitingdevice connected to said pressure medium chamber.
 11. In a cold chamberpressure casting machine, the improvement claimed in claim 10, in whichsaid insert is formed with a measuring chamber having an open endcommunicating with said pressure medium chamber adjacent the open end ofthe latter, and having its opposite end connected with and communicatingwith said pressure limiting device.
 12. In a cold chamber pressurecasting machine, the improvement claimed in claim 3, in which saidpressure medium is a protective gas.
 13. In a cold chamber pressurecasting machine, the improvement claimed in claim 4, in which saidpressure medium supply line is a passage formed in the lateral wall ofsaid insert; said opening communicating with said pressure mediumchamber.
 14. In a cold chamber pressure casting machine, the improvementclaimed in claim 4, in which said pressure followup valve is set to afixed pressure value.
 15. In a cold chamber pressure casting machine,the improvement claimed in claim 4, in which the upper wall of saidinsert is formed with a closable opening above the operating level ofthe melt.
 16. In a cold chamber pressure casting machine, theimprovement claimed in claim 15, including a float in said crucible inthe range of the operating level of the melt and controlling saidclosable opening.